Carbon dioxide liquification plant and process



APril 1966 T. R. BLEVINS, JR 3,243,967

CARBON DIOXIDE LIQUIFICATION PLANT AND PROCESS Filed Nov. 20, 1963 Theodore E. 5/6 v/ns, Jr

A TTORNEY United States Patent 3,243,967 CARBQN DIOXEDE LIQUIFICATION PLANT AND PRGCESS Theodore R. Blevins, J12, Arvada, C010,, assignor to Continental Gil Company, Ponca City, Okla, a corporaion of Gklahoma Filed Nov. 20, 1963, Ser. No. 325,113 3 Clmms. (Cl. 629) This invention relates to a process and apparatus for liquefying gas and particularly for liquefying carbon dioxide.

An object of the invention is a process for liquefying gas, especially carbon dioxide, without the need for elaborate refrigeration means. Another object of the invention is apparatus for liquefying gas, especially carbon dioxide, which does not involve elaborate refrigeration means. A particular object of the invention is an apparatus for liquefying gas, especially carbon dioxide, wherein liquefied gas can be automatically transferred from an accumulator to a storage tank without the use of a pump. Another particular object of the invention is apparatus which permits liquefying gas, particularly carbon dioxide, and transfer of liquefied gas periodically from an accumulator to a storage tank without the use of a pump or operator control. Other objects of the invention will become apparent in the course of the detailed description thereof.

The single figure shows the essential items of apparatus and of process flow for the practice of the invention by a preferred embodiment thereof.

Briefly, the process of the invention comprises: passing an expanding gaseous stream in indirect heat exchange with a second gaseous stream which second gaseous ream is maintained at substantially constant elevated pressure while the heat exchange is being controlled to liquefy at least a substantial proportion of the second gaseous stream to produce a product stream containing at least a substantial proportion of liquefied gas; this product stream is withdrawn from the heat exchange zone at substantially the same pressure as maintained therein. An additional amount of liquefied gas can be obtained by expanding the product s eam from the withdrawal pressure to a lower pressure.

The above and other features of the invention are described in connection with the single figure which forms a part of the specification. It is to be understood that the figure sets forth only those items of apparatus and those process features needed for the practice of the invention, to be taken in conjunction with features which can be readily added by those of ordinary skill in this art.

The invention is described in connection with liquefication of carbon dioxide; however, it is to be understood that the process and apparatus may be used for liquefying any gas whose phase diagram permits a substantial amount of liquid to be produced under the process conditions of the invention.

A gaseous stream of carbon dioxide, at a predetermined elevated pressure, is passed from source 11 by way of valved conduit 12 into heat exchanger 13. Another gaseous carbon dioxide stream from source 15 is passed, at a predetermined elevated pressure, by way of valved line 16 into heat exchanger 13 separately from the gaseous stream introduced by way of line 12.

The carbon dioxide streams here may be obtained from any source. They are particularly easily obtainable from the waste gas of natural gas purification plants. The carbon dioxide streams are dehydrated to a dew point where condensation of water vapor will not interfere with operation of the process. The streams may be available "ice at elevated pressures or brought to the desired elevated pressure by compressors, not shown. The carbon dioxide may be pure or it may contain moderate amounts of natural gas hydrocarbons.

Heat exchanger 13 is adapted for indirect heat exchange contact between two gaseous streams. Preferably heat exchanger 13 is a shell and tube exchanger. The dimensions of the heat exchanger will be dependent upon the heat duty required to liquefy at least a substantial proportion of the gaseous stream from source 15.

The cooling heat exchanger duty is afforded by expanding the gaseous stream from line 12 through heat exchanger 13 down to the necessary lower pressure. In this embodiment the expanded gas is vented to the atmosphere by way of valved line 18. In general, the main expansion of the gas stream from source 11 is carried out before the stream enters exchanger 13. Additional ex pansion is taken within exchanger 13. The gaseous stream from source is cooled in heat exchanger 13 at substantially constant pressure which pressure generally is about the same pressure as that existing on the gas stream delivered from source 15, except for line pressure drops.

A gas liquid product stream is produced in heat exchanger 13 by the substantial constant pressure cooling; this product stream is withdrawn from heat exchanger 13 by way of line 20. Pressure regulator 22 maintains the withdrawn product stream and the gas from source 15 at the substantially constant desired elevated pressure. The heat exchange within exchanger 13 is carried out in such a manner that at least a substantial proportion of the gaseous stream is liquefied. With a carbon dioxide gaseous stream it is convenient to liquefy 20-50% of the gas introduced by way of line 16 into exchanger 13.

In a preferred form of the invention, an additional amount of liquid carbon dioxide is produced by expansion cooling of the product stream beyond regulator 22. The stream of gas and liquid is passed from regulator 22 and expands through conduit 24 to the pressure maintained within gas-liquid separator vessel (accumulator) 30. Accumulator 3% may be any vessel which affords separation of a gas-liquid stream and permits accumulating a body of liquid and the withdrawal overhead of gas. Gas is taken overhead from accumulator 33 by way of conduits 34, 35 and 36. The desired substantially constant elevated pressure is maintained within accumulator by pressure regulator 38 positioned in conduit 36. Conduits 34, 35 and 36 permit passing the elevated pressure gas from accumulator 30 to join the gas stream from conduit 12 near the entrance of heat exchanger 13. This return gas provides additional expansion cooling.

Accumulator 30 is provided with a liquid level sensing and control means 49. LLC 40 may be any form of conventional means responsing to the liquid level. The sensing element here is a simple float.

Conduit 44 permits transfer of liquid carbon dioxide from accumulator 39 to storage tank 46. An important feature of the process of the invention is that the liquid from accumulator 3th is transferred by way of line 44 to storage tank 46 without the use of a pump.

Normally accumulator 3%, storage tank 46 and all of the lines and vessels are insulated; for convenience no insulation is shown.

Preferably tank 46 is maintahe at subsantially the same pressure as acumulator 3%). In this embodiment gas produced in tank 46 is used for expansion cooling in heat exchanger 13 by providing conduit Eli and conduit 52 which joins conduit 36. Conduit 52 is provided with a check valve, not numbered. In the embodiment of the figure pressure regulator 38 normally maintains .and 4% of natural gas hydrocarbons.

additional expansion takes place.

,from exchanger 13 at 50 F.

tank 46 and acumulator 30 at substantially the same pressure.

When a sufficient body of liquid is present in accumulator 30, it is transferred by way of conduit 44 to tank 46 by the creation of a pressure difierential between accumulator 30 and tank 46. The pressure in tank 46 i's'lowered below the pressure of accumulator 3t) and this pressure dilferential forces liquid from accumulator 30 into tank 46. This pressure differential may be created by providing a simple relief valve at tank 46 and venting the gas to the atmosphere.

However, an important feature of this invention is "that liquid is periodically, automatically, transferred from accumulator to tank 46 without wasting the expansion cooling capacity possessed by gas from tank 46. In this embodiment a bypass conduit means 60 is provided for passing gas from conduit 50 around pressure regulator 38 to conduit 36. Conduit 69 includes control valve 62 which is activated by LLC 40 by way of control line 64. When the float reaches the desired liquid level in accumulator 30, the liquid level controller 40 activates the valve opening mechanism of value 62 causing it to open. Gas from tank 46 is then passed through conduit 50 and conduit 62 into line 36 which is at a much lower pressure than accumulator 30. Thus the necessary pressure differential between accumulator 3t and storage tank 46 is created and liquid is forced from accumulator until LLC 40 causes valve 62 to close.

The process of the invention is described in connection with FIG. 1 in a specific embodiment wherein essential- 1y pure liquid carbon dioxide is produced from a gaseous stream consisting of 92% carbon dioxide, 4% nitrogen, A natural gas purification plant provides 4 million standard cubic feet per day of this gas. This stream is dehydrated to a dew point lower than 50 F.; the dry gas stream is at 600 p.s.i.g. and 64 F. This 600 p.s.i.g. stream is expanded and is introduced into heat exchanger 13 where The stream emerging from heat exchanger 13 is at about F. and about p.s.i.g.

- The stream which provides the liquid carbon dioxide F. temperature. 1.4 million s.c.f. per day of this gas are introduced at 60 F. and 820 p.s.i.g. into exchange 13 where it is indirectly cooled; a product stream emerges This gas stream is maintained in exchanger 13 at 810 p.s.i.g. by controller 22.

The stream emerging from exchanger 13 by way of line 20 contains about 50% of liquid carbon dioxide.

About 15% more of the gaseous carbon dioxide present in the product stream is liquefied by expansion cooling down to 300 p.s.i.g., which pressure is maintained at accumulator 30 by regulator 38. Tank 46 is maintained at 300 p.s.i.g. and a tempertaure of 10 F.

When the liquid level in accumulator 30 reaches the desired point, valve 62 is opened, pressure drops in tank 46 and the pressure differential between accumulator 30 and tank 46 automatically transfers liquid to tank 46. Valve 62 is closed by LLC 40 and the cycle of accumulation of liquid in accumulator 3%) begins again.

Means not shown are provided in accumulator 30 which automatically close-in the operation should the liquid level in accumulator 30 reach a danger point.

It can be seen from the above description that the invention provides a very simple answer to producing liquids gas when gas is available at high pressure in amounts greater than that needed in the form of a liquid; the extra gas is used to provide the cooling needed to produce the desired amount of liquid gas. In natural gas purification plants where it is customary to operate with a minimum labor force, the apparatus and process of this invention provide an operation that functions automatically without the need for intervention by an operator except for maintenance.

product is available at a pressure of 820 p.s.i.g. and 60.

Thus having described the invention what is claime 1. A process for liquefying gas and transferring said liquid to a storage tank which process comprises:

indirectly heat exchanging a gaseous stream, maintained at substantially constant pressure by a first pressure regulator means, and another gaseous stream under conditions Wherein'expansion of said other stream provides suflicient cooling-to liquefy at least a substantial proportion of said constant pressure stream;

passing a liquid-vapor product stream, at substantially the aforesaid constant pressure, from said heat exchange to a gas-liquid accumulator adapted to accumulate liquefied gas while maintaining said ac cumulator at a substantially constant pressure, lower than the aforesaid pressure;

expansion cooling said product stream through said first regulator means during said passage to liquefy additional gas;

passing gas from said accumulator and gas from a storage tank containing liquefied gas, transferred from said accumulator, at said accumulator constant pressure, through another pressure regulator means to said indirect heat exchange as a part of said other gaseous stream; and periodically transferring liquid from said accumulator to said tank, by having an accumulator liquid level controller means activate a gas control valve means, in communication with the gas space in said tank, thereby afiording a pressure differential between said accumulator and said tank. 4

2. The process of claim 1 wherein both said streams are carbon dioxide.

3. An apparatus for liquefying a gas which apparatus comprises, in combination:

heat exchanger means for indirect contact of two gaseous streams;

a first conduit means for passing a first gaseous stream at predetermined elevated pressure into said heat exchanger means and means permitting expansion cooling of said first stream to provide cooling duty in said exchanger;

a second conduit means for introducing a second gaseous streams, at a predetermined elevated .pressure, into said heat exchanger and means for maintaining said second stream at substantially constant pressure while in said heat exchanger;

a gas-liquid separator-accumulator and means for maintaining said vessel at a predetermined elevated pressure; j

a third conduit means for passing a gas-liquid stream, product of said heat exchanged second stream, into said accumulator;

a storage tank for liquefied gas;

a fourth conduit means for passing liquefied gas from said accumulator to said tank;

a fifth conduit means for passing gas from said accumulator to said heat exchanger means for indirect contact with said second stream in said exchanger;

a sixth conduit means for passing gas from said tank to join gas from said accumulator, at the predetermined elevated pressure maintained in said accumulator; and I a bypass conduit means, including valve means responsive to liquid level within said accumulator, for passing gas from said tank to said heat exchanger for indirect contact with said second stream in said exchanger, said bypass conduit means providing a pressure drop between said accumulator and said tank, whereby liquefied gas can be automatically forced from said accumulator to said tank.

(References on following page) References Cited by the Examiner UNITED FOREIGN PATENTS STATES PATENTS 579,624 6/ 1933 Germany. Ragatz 202-460 XR 1,145,197 3/1963 Germany. Eastman 62-11 5 301,741 12/1929 Great Britain. BronsonL 62--10 Gantt 202160 NORMAN YUDKOFF, Primary Examiner. 

1. A PROCESS FOR LIQUEFYING GAS AND TRANSFERRING SAID LIQUID TO A STORAGE TANK WHICH PROCESS COMPRISES: INDIRECTLY HEAT EXCHANGING A GASEOUS STREAM, MAINTAINED AT SUBSTANTIALLY CONSTANT PRESSURE BY A FIRST PRESSURE REGULATOR MEANS, AND ANOTHER GASEOUS STREAM UNDER CONDITIONS WHEREIN EXPANSION OF SAID OTHER STREAM PROVIDES SUFFICIENT COOLING TO LIQUEFY AT LEAST A SUBSTANTIAL PROPORTION OF SAID CONSTANT PRESSURE STREAM; PASSING A LIQUID-VAPOR PRODUCT STREAM, AT SUBSTANTIALLY THE AFORESAID CONSTANT PRESSURE, FROM SAID HEAT EXCHANGE TO A GAS-LIQUID ACCUMULATOR ADAPTED TO ACCUMULATE LIQUEFIED GAS WHILE MAINTAINING SAID ACCUMULATOR AT A SUBSTANTIALLY CONSTANT PRESSURE, LOWER THAN THE AFORESAID PRESSURE; EXPANSION COOLING SAID PRODUCT STREAM THROUGH SAID FIRST REGULATOR MEANS DURING SAID PASSAGE TO LIQUEFY ADDITIONAL GAS; PASSING GAS FROM SAID ACCUMULATOR AND GAS FROM A STORAGE TANK CONTAINING LIQUEFIED GAS, TRANSFERRED FROM SAID ACCUMULATOR, AT SAID ACCUMULATOR CONSTANT PRESSURE, THROUGH ANOTHER PRESSURE REGULATOR MEANS TO SAID INDIRECT HEAT EXCHANGE AS A PART OF SAID OTHER GASEOUS STREAM; AND PERIODICALLY TRANSFERRING LIQUID FROM SAID ACCUMULATOR TO SAID TANK, BY HAVING AN ACCUMULATOR LIQUID LEVEL CONTROLLER MEANS ACTIVATE A GAS CONTROL VALVE MEANS, IN COMMUNICATION WITH THE GAS SPACE IN SAID TANK, THEREBY AFFORDING A PRESSURE DIFFERENTIAL BETWEEN SAID ACCUMULATOR AND SAID TANK. 